The objective of this trial is to assess the efficacy and safety in relation to placebo, in patients with osteoarthritis of the knee, over 3 years. This will be a multicenter, randomized, double--blind, placebo controlled, parallel group study exploring treatments of BAY 12-9566 at two dose levels for 3 years: 400 mg/day and 100 mg/day. Participants in this study will be patients with mild to moderate symptomatic osteoarthiritis of the knee on currently available background OA medications. The overall design of the study consists of a 2 week screening period and a 3 year treatment period. The estimated duration of the study is 36.5 months, with a 12 month enrollment period, for a total of 48.5 months. The intent is to enroll approximately 879 patients into the study at 60 centers (293 patients per treatment group) in anticipation of 573 valid patients. Patients who drop out will not be replaced. WOMAC (questionnaire) & analgesic usage (patient diary) will be collected at baseline and every 3 months. Duplicate radiographs of the knee in the semi-flexed position will be obtained at baseline and at 12, 18, 24, 30, & 36 months. MRI of the knee will be performed at baseline, and each 12 months on a subset of patients. Plasma and urine samples for biological marker assays will be collected predose, during the study and after the last dose. Participants will be monitored for safety by means of physical examination, vital signs, and clinical laboratory tests. The applicants role in this study is to serve as one of the centers, with a recruitment goal of 15-21 participants. We will also function as an administrative 'hub', coordinating and providing both radiology and MRI assessments for participants at three local sites.